An ignition device for an internal combustion engine receives an ignition signal by an igniter circuit block from an electronic control unit (ECU) and supplies an ignition condition signal (for example, failure signal) from the igniter circuit block thereby responding to the ECU (for example, patent document 1). Further, similar technologies are disclosed in patent documents 2 and 3.    (Patent document 1) JP 8-128381A (U.S. Pat. No. 5,571,245)    (Patent document 2) JP 2004-36438A (US 2004/0011342)    (Patent document 3) JP 2004-197730A
One such a circuit example is shown in FIG. 17. As shown in FIG. 17, an ignition device 101 for an internal combustion engine (not shown) is provided with an igniter 102, an ignition coil 3 and a diode 4 connected in the shown configuration and energizes the ignition coil 3 in response to an ignition signal IGt supplied from an ECU 5 for activating a spark plug 6.
In the igniter 102, a switching element such as an IGBT and a temperature detection diode (not shown) for detecting the temperature inside the IGBT are provided. The gate drive of the IGBT is shut off, when it is determined based on the voltage-temperature characteristic of the temperature detection diode that the IGBT is in the over-temperature condition. This gate drive shut-off function is referred to as a lock inhibition function. With this lock inhibition function, the temperature of the IGBT is decreased to protect the IGBT from over-temperature breakdown.
FIG. 18A shows an example of detection of the temperature inside the igniter and the lock inhibition function, and FIG. 18B shows in a time chart form a basic operation of the lock inhibition function and inhibition release processing.
As shown in FIG. 18A, the igniter 102 is provided with a temperature detection circuit 114 and a latch circuit 115. In the normal operation, the temperature detection circuit 114 detects the temperature of the IGBT. Since the temperature detection circuit 114 detects that the temperature of the IGBT is low in the normal operation, a normal drive signal voltage VG is applied to the gate of the IGBT in response to the ignition signal IGt (time t0 in FIG. 18B). When the temperature detection circuit 114 detects that the temperature of the IGBT rises to be higher than a predetermined temperature (that is, the voltage Vf of the built-in diode in the IGBT falls to be lower than an over-temperature reference Vref), a set signal is applied to the set terminal S of the latch circuit 115.
The latch circuit 115 produces a lock output Lck to shut off the gate drive signal (time t1 in FIG. 18B), when the set signal is applied from the temperature detection circuit 114. The lock output Lck indicates that the current supply to the IGBT is too much. Thus, the IGBT is protected from breakdown by shutting off supply of a current I1, which flows in the IGBT.
Since a power-off command signal is applied to the reset terminal R of the latch circuit 115 as shown in FIG. 18A, the lock condition is released when power supply of a battery +B is turned off as shown in FIG. 18B (time t2).
However, once the igniter 102 has become abnormal and locked, it is only possible to release the lock by turning off the power supply. It is not convenient to release the lock of the igniter 102 by the ECU 5. For example, the power supply must be turned of to restart the internal combustion engine, each time the igniter 102 is locked by an abnormality signal produced temporarily at time of engine starting or the like.